It has been known to use a sulfur print testing method to detect the segregation and the distribution of sulfur in steel. In that sulfur print testing method, photographic paper soaked with a sulfuric acid solution is attached to the surface to be tested, such as a cross-section of a slab. However, this method involves a problem in that it requires a considerable amount of time to polish the surface to be tested, because a very smooth surface is required in this method. Also, it is a problem in this method that only sulfur is mainly detected, and no inclusions other than sulfur can be directly detected. Although, formerly, aluminum and manganese could be indirectly detected using the result of the detection of alumina (Al.sub.2 O.sub.3) and manganese detected by the sulfur print testing method, difficulties have been increased in such indirect detection because the concentration of sulfur in steel has been reduced recently.
It has also been known to use the X-ray micro analyser method for the measurement of the inclusions in a specimen, by which method various inclusions present on the surface to be tested are directly detected. In this method, an electron beam having a very small diameter, for example, with a diameter between approximately 1 .mu.m and 10 .mu.m, is irradiated onto the surface to be tested. The X-rays emitted from the inclusions due to the irradiation of the electron beam are detected, so that the elements and the quantities of the inclusions are determined two-dimensionally. However, this method includes a problem in that the detector is located lower than the specimen to be tested, due to the use of an analyzing crystal having a curved surface, and hence, the size of the specimen is limited, so that only specimens having a size smaller than 20.times.20 mm.sup.2 can be used. In such specimens of small size, only a small length, on the order of a few millimeter, is scanned mechanically and cannot be scanned by electron beam due to use of an analytical crystal having a curved surface. Accordingly, in this method, such a wide area detection as in the case of the sulfur print testing method cannot be effected. Also, again it is a problem in this method that it requires a considerably amount of time to polish the surface to be tested, because a smoothness which is similar to the smoothness required for specimens for an electron microscope is required for a specimen for this method.
The present invention has been proposed in order to solve the above described problems in the prior art methods.